Artificial or synthetic marble is a general designation for various types of materials used as building products, such as bathroom vanity tops, sinks, shower stalls and kitchen counter tops, and other decorative surfaces. It is also a suitable material for use in furniture, lining materials, and in stationary small articles. The artificial marble is easily kept clean and neat. Therefore, it has increasingly been used in hospitals, nursing homes, as well as in commercial and residential food preparation facilities.
Artificial marbles encompass cultured marble, onyx and solid surface materials typically comprising some kind of resin matrix and either with or without a filler present in the resin matrix. Typically, cultured marble is made of a gel coating of unfilled unsaturated polyester on a substrate of a filled unsaturated polyester. The filler may be calcium carbonate or a similar material. Onyx typically consists of a gel coat of unfilled unsaturated polyester on a substrate of filled unsaturated polyester. The filler in this case is typically alumina trihydrate (ATH). Solid surface materials are typically filled resin materials and, unlike cultured marble or onyx, do not have a gel coat. Corian® material available from E. I. du Pont de Nemours and Company (DuPont), Wilmington, Del., is a solid surface material comprising an acrylic matrix filled with ATH. Another solid surface DuPont material, known by the brand name Zodiaq®, is alternatively described as an engineered stone or artificial granite. Such materials are made from an unsaturated polyester matrix filled with quartz or other similar fillers.
As evidenced by numerous materials in the market, there is clearly a demand for materials and/or processes that either minimize or kill harmful microorganisms encountered in the environment. Such materials are useful in areas for food preparation, processing, service or handling. Such materials will also be useful in areas for personal hygiene, such as bathroom facilities. Similarly, there is a use for such antimicrobial materials in hospitals and nursing homes where people with lowered resistance are especially vulnerable to pathogenic microorganisms.
Solid surface materials made of either an acrylic resin, an unsaturated polyester resin, an epoxy resin, or other such resins and incorporating certain antimicrobial agents throughout the resin are described in WO 97/49761 (E. I. du Pont de Nemours and Company). However, such antimicrobial agents can be expensive, resulting in a high installation cost for the resulting solid surface material.
Chitosan and chitosan-metal compounds are known to provide antimicrobial activity as bactericides and fungicides (see, e.g., T. L. Vigo, “Antimicrobial Polymers and Fibers: Retrospective and Prospective,” in Bioactive Fibers and Polymers, J. V. Edwards and T. L. Vigo, eds., ACS Symposium Series 792, pp. 175-200, American Chemical Society, 2001). Chitosan is also known to impart antiviral activity, though the mechanism is not yet well understood (see, e.g., Chirkov, S, N., Applied Biochemistry and Microbiology (Translation of Prikladnaya Biokhimiya i Mikrobiologiya) (2002), 38(1), 1-8).
Chitosan is the commonly used name for poly-[1-4]-β-D-glucosamine. Chitosan is chemically derived from chitin (a poly-[1-4]-β-N-acetyl-D-glucosamine) which, in turn, is derived from the cell walls of fungi, the shells of insects, and, especially, crustaceans. Thus, it is inexpensively derived from widely available materials. It is available as an article of commerce from, for example, Primex (Iceland); Biopolymer Engineering, Inc. (St. Paul, Minn.); Biopolymer Technologies, Inc. (Westborough, Mass.); and CarboMer, Inc. (Westborough, Mass.). Chitosan can also be treated with metal-salt solutions so that the metal ion forms a complex with the chitosan. For example, U.S. Pat. Nos. 5,541,233 and 5,643,971 disclose a process for preparing durable antimicrobial agents by treating a chitosan suspension with metal salts of zinc and copper followed by chelation of a potentiator such as an imidazole. Application WO 99/37584 discloses the preparation of chitosan-zinc sulfate, copper sulfate and silver nitrate complexes for treating water to reduce levels of pathogens.
In commonly assigned U.S. Patent Application No. 60/290,297 (filed 11 May 2001), chitosan (in the form of an acidic solution applied to polyester articles) is shown to impart antimicrobial activity. The chitosan-treated article may be treated subsequently with a solution of zinc sulfate, cupric sulfate, or silver nitrate to enhance antimicrobial activity.
Cultured marbles have been developed incorporating an antimicrobial agent in the gel coat only (i.e., not throughout the matrix of the substrate). Such materials have been disclosed in Japanese Patent Application Publication Kokai: 7-266522. These materials have a relatively thin gel coat, typically on the order of 15 mils. As such, when the gel coat is depleted of antimicrobial agent or the gel coat wears away or is otherwise removed, the antimicrobial effect of the gel coat is significantly decreased or lost entirely.
The problem that remains to be solved is to provide solid surface materials comprising either an acrylic resin, an unsaturated polyester resin, an epoxy or other similar resin and an effective antimicrobial agent dispersed throughout the resin.